Added example on how to handle unions.

1 files changed, 92 insertions, 0 deletions

diff --git a/example_unions/decode.c b/example_unions/decode.c
new file mode 100644
index 00000000..b20df84e
--- /dev/null
+++ b/example_unions/decode.c
@@ -0,0 +1,92 @@
+/* This program reads a message from stdin, detects its type and decodes it.
+ */
+ 
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include <pb_decode.h>
+#include "unionproto.pb.h"
+
+/* This function reads manually the first tag from the stream and finds the
+ * corresponding message type. It doesn't yet decode the actual message.
+ *
+ * Returns a pointer to the MsgType_fields array, as an identifier for the
+ * message type. Returns null if the tag is of unknown type or an error occurs.
+ */
+const pb_field_t* decode_unionmessage_type(pb_istream_t *stream)
+{
+    pb_wire_type_t wire_type;
+    int tag;
+    bool eof;
+
+    while (pb_decode_tag(stream, &wire_type, &tag, &eof))
+    {
+        if (wire_type == PB_WT_STRING)
+        {
+            const pb_field_t *field;
+            for (field = UnionMessage_fields; field->tag != 0; field++)
+            {
+                if (field->tag == tag && (field->type & PB_LTYPE_SUBMESSAGE))
+                {
+                    /* Found our field. */
+                    return field->ptr;
+                }
+            }
+        }
+        
+        /* Wasn't our field.. */
+        pb_skip_field(stream, wire_type);
+    }
+    
+    return NULL;
+}
+
+bool decode_unionmessage_contents(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
+{
+    pb_field_t field = {}; /* NB: Could get rid of this wrapper by fixing issue #2. */
+    field.ptr = fields;
+    
+    return pb_dec_submessage(stream, &field, dest_struct);
+}
+
+int main()
+{
+    /* Read the data into buffer */
+    uint8_t buffer[512];
+    size_t count = fread(buffer, 1, sizeof(buffer), stdin);
+    pb_istream_t stream = pb_istream_from_buffer(buffer, count);
+    
+    const pb_field_t *type = decode_unionmessage_type(&stream);
+    bool status = false;
+    
+    if (type == MsgType1_fields)
+    {
+        MsgType1 msg = {};
+        status = decode_unionmessage_contents(&stream, MsgType1_fields, &msg);
+        printf("Got MsgType1: %d\n", msg.value);
+    }
+    else if (type == MsgType2_fields)
+    {
+        MsgType2 msg = {};
+        status = decode_unionmessage_contents(&stream, MsgType2_fields, &msg);
+        printf("Got MsgType2: %s\n", msg.value ? "true" : "false");
+    }
+    else if (type == MsgType3_fields)
+    {
+        MsgType3 msg = {};
+        status = decode_unionmessage_contents(&stream, MsgType3_fields, &msg);
+        printf("Got MsgType3: %d %d\n", msg.value1, msg.value2);    
+    }
+    
+    if (!status)
+    {
+        printf("Decoding failed.\n");
+        return 1;
+    }
+    
+    return 0;
+}
+
+
+